Organic light emitting diode devices, or OLED devices, are generally known in the art. An OLED device typically includes one or more organic light emitting layer(s) disposed between electrodes. For example, first and second electrodes, such as a cathode and a light transmissive anode are formed on a substrate. Light is emitted when current is applied across the cathode and anode. As a result of the electric current, electrons are injected into the organic layer from the cathode and holes may be injected into the organic layer from the anode. Electrons and holes generally travel through the organic layer until they recombine at a luminescent center, typically an organic molecule or polymer. The recombination process results in the emission of a light photon usually in the visible region of the electromagnetic spectrum.
The layers of an OLED are typically arranged so that the organic layers are disposed between the cathode and anode layers. As photons of light are generated and emitted, the photons move through the organic layer. Those that move toward the cathode, which generally comprises a metal, may be reflected back into the organic layer. Those photons that move through the organic layer to the light transmissive anode, and finally to the substrate, however, may be emitted from the OLED in the form of light energy. Light transmissive anodes have been composed of substantially transparent nonmetallic conductive materials, such as indium tin oxide. Of course, additional, optional layers may or may not be included in the light source structure.
For many purposes, one may desire light emitting or OLED devices to be generally flexible, i.e., are capable of being bent into a shape having a radius of curvature of less than about 10 cm. These light emitting devices are also preferably large-area, which means they have a dimension of an area greater than or equal to about 10 cm2, and in some instances are coupled together to form a generally flexible, generally planar OLED panel comprised of one or more OLED devices, which has a large surface area of light emission. Such panels should be hermetically sealed since moisture and oxygen have an adverse impact on the OLED device. It is desired that an electrical pathway be established with the light emitting panel, and also that the electrical pathway maintain flexibility, be easily and accurately positioned, establish good electrical continuity, and maintain a thin profile.
However, especially for large area OLED panels, it is also generally desired to ensure that the brightness of such panels be uniform, since nonuniformity can sometimes be sensed visually. One known possible failure mode includes ingress of moisture and/or oxygen over time. The effect of moisture and oxygen ingress may sometimes be visually observed as dark spots that form in the light emitting area. Good adhesive sealing methods and barrier methods, as well as gettering, have served well to mitigate this failure mode.
Nevertheless, it may be desirable to minimize other factors which can detract from the light output and aesthetic appearance of large area, planar, flexible OLED devices.